wow... backfire or shotgun blast!

[wrook1984]

So, I'm getting thoroughly frustrated now. I've put in new spark plugs, I have good compression, I've cleaned the carbs, I've drained and put in new gas, I removed the air box cause it was pissing me off and wasn't making a difference anyway, used some starting fluid to try and kick things off (I know, that's probably why you'll say it's doing this, but it was doing it with just gas too)
So here's my problem.

My 86 FZ600 isn't starting, hasn't started yet since I've owned it (about a month) and once I think I have it all ready to roll, I try to start it and it just cranks, then cranks some more, but isn't lighting off. The starter is working awesome, and the battery is new. So i crank it a little more, and BOOM! the thing backfires out of the exhaust pipe so loud it sounds like a shotgun and I'm afraid the neighbors are going to call the cops. Seriously. But I don't stop there, oh no! I think, okay, it just got flooded for some reason, so I turn off the gas and crank it a little more, hoping to drain the excess fluid, then I use a little (very little) starting fluid to try and get it to just rev for a second, do I get even that? NO! it backfires again, really freakin loud! my ear is ringing.

So, has anyone else run into this problem before? I've bought two repair manuals and they all say the cylinders are lables 1, 2, 3, 4 going from left to right as you sit on the bike. They also say the first ignition coil fires cylinder 1 and 4 and the right hand ignition coil fires cylinder 2 and 3. Plus the plug wires are labeled. I have compression (obviously note the backfire) and good spark and am reasonably confident I have the wires in the correct order.

So does anyone have any advice or ideas for me? I'd love to get this bike running but if I can't I'll most likely sell it and move on to another FZ, problem is that won't be for a while, I'm an intern and a full time student so funds are low.

HELP!!!


thanks

 

[Motogiro]

If I were in the same situation I would think it could be timing. If you have established that the compression is good and you have spark. It could be timing. Of course timing in the valve train could be also off but I would think if it were that far off you'd have bad compression. There is prolly a sensor that tells when to fire the ignition module and it could be set wrong or defective.
Keep in mind I'm kinda shot gunning ideas on this cuz I don't have any specs. on your bike.
Edit: Are you getting a raw gas smell when you crank it without adding gas or starter fluid?

 

[Jblk9695]

Sounds to me like the cam timing is off. Unfortunately the only way to check that is to pull the valve cover and check the cam timing marks. I might be wrong as these motors might be the interference type and if the cams were off the valves would hit the pistons so I'm probably all wet. Does the motor have solid state ignition or points, either way the ignition timing could be off also, never know what the PO might have done. Just my $.02 worth.
Hope you find the problem.

Jerry

 

[Jblk9695]

If I were in the same situation I would think it could be timing. If you have established that the compression is good and you have spark. It could be timing. Of course timing in the valve train could be also off but I would think if it were that far off you'd have bad compression. There is prolly a sensor that tells when to fire the ignition module and it could be set wrong or defective.
Keep in mind I'm kinda shot gunning ideas on this cuz I don't have any specs. on your bike.

LOL, came up with the same idea a nano second apart:thumbup:

Jerry

 

[Neilio]

Too much backpressure form the exhaust system? No clue really, just a shot in the dark.

 

[champion221elite]

Engines need 3 things at the correct time to operate properly.

1. Fuel
2. Compression
3. Spark

Of the 3 items, you have fuel and compression... that's good. If you have spark, that's good. Even more important than having spark, is having spark at the right time.

Even with compression and fuel, a spark at the wrong time might well explain your backfire situation and inability to get the bike running. In effect, if your ignition timing is off, your sparkplug could be discharging at BDC or anywhere else throughout the cycle. This could allow fuel to puddle and build to the point that it explodes and creates a backfire. Not only is the ignition timing important, the quality of spark is also important. An orange colored, weak spark might not be of sufficient quality to properly ignite the fuel charge.

If you have a manual for your bike, it should outline ways to check your valvetrain timing as well as ignition timing. Given the 3 components of a running engine, (fuel, compression, spark) the weakest link is your electrical (ignition) system. Your problem will likely be found there.

 

[Fred]

A backfire doesn't prove that you have compression. A backfire is an explosion in the exhaust system, so it only proves that you have an exhaust pipe.

But engines without compression generally don't backfire, or do much of anything, so I'll assume compression is OK.

My first guess is that the ignition system has gone wonky, either due to bad plug wires or plain old electrical gremlins.

It's also possible that the carbs still have problems. If the float needles are worn and leaking, then the carbs will overflow and pour fuel into the engine, flooding it.

I would remove all four plugs immediately after trying to start the bike. See if they are wet or smell like gasoline. If they are, then the engine is flooding and you'll need to tear into the carbs again to replace parts.

If the plugs are dry, then move on to testing the ignition system for good spark. With the plugs removed from the engine, hook them up to the plug wires where you can see them all. Use jumper wires to ground each spark plug to the engine block or frame. Crank the engine and see if all four plugs are sparking strongly and regularly.

See my CX500Turbo video for an example of this test done on a different bike. [ame=http://www.youtube.com/watch?v=M2HtHyqIwRo]YouTube - CX500T Resurrection, Day 2[/ame]

Do these tests and let us know what you find.

Fred

 

[Fred]

OK, nevermind that test. Here's your real problem, I think. From another of your posts:

http://www.600riders.com/forum/usa-...-some-help-thanks-advance-too.html#post340243

I also cleaned out the carbs (not as thouroughly as I should but it'll suffice I think) took off the top diaphram and cleaned from there so I wouldn't have to remove the whole carb setup again, which was a pain to install w/ the air box.

You did not clean the important parts of the carb if all you did was remove the diaphrams and spray in carb cleaner. You have got to remove the carbs from the bike and remove the float bowls. You then have to remove the main jets and emulsion tubes and most importantly remove the idle jets. All of these will need to be cleaned until you can see light through all the holes in them. The idle jets especially have very small holes and will easily clog up with old fuel.

Then spray carb cleaner through every passage you find on the carb. For each passage, make sure that the cleaner you spray into the hole comes out at another hole. There are no dead end passages in the carbs.

On an engine that old, you will need new float bowl gaskets. And it would not be a bad idea to change out the float needles while you're at it. They usually have rubber tips and as those tips get old and hard, they begin to leak fuel and flood the carbs.

Fred

 

[wrook1984]

Holy Crap guys! Awesome help so far, haven't had a chance to test the theories yet, but I'm getting there. BTW I've decided to remove the air box for good and go w/ the pod style just for the room.
Yeah, I've come back around to the carb cleaning solution myself, thanks Fred. I'll need to find a rebuild kit or whatever I can find I guess. I know it's getting some gas and the carb cleaning/rebuild I can attempt myself whereas the timing is factory set and I'll need to take it in, I'll have to look into it if nothing else works. Thanks again guys, I'll keep you posted as I find time to tinker, maybe if I'm really lucky I'll get a ride organized to try it out before the nice weather leaves us , I know some good roads to carve around King County.

 

[lonesoldier84]

Wow. Got nothing of note to add, except:

GOOD LUCK.

Hope it works out well. In the end you will be in love with yourself for fixing it (and not copping out and taking it to a dealer like I do).

 

[wrook1984]

Well, it's not the carbs, it's gonna be a timing issue or like someone said, some electrical gremlins making my life hell (I did actually find a short in the turn signal circuit so I just removed that fuse, it'll still crank w/out it so maybe that's just a bad omen)....so anyway I posted the bike on Craigslist and I'll just save up for a newer FZ6 with the Delta One frame and the slanted motor (faster and more nimble anyway)
Thanks for all the help guys! I just don't want to spend the bucks to take it to a dealership or mechanic and put more money into the bike than it's worth.
If you want to see what the bike looks like now, just check out my pics.
Thanks again for the help!